The need for improved microwavable food packaging materials persists as the number and types of microwavable foods increases. According to a report from Global Industry Analysts, the global consumer market for microwavable foods continues to grow and is forecast to reach $91 billion in 2015.
Packaging for microwavable food is typically made from plastic materials. The Food and Drug Administration (FDA) establishes regulations and testing standards for food containers and food packaging. Packaging manufacturers must disclose the chemical nature of the container or film, the components, as well as any potential health hazards. In addition, the FDA tests food contact surfaces for migration of polymers, and polymer additives into food. FDA approval of a packaging container or food wrapping film ensures that the packaging container or wrapping film is safe for use as a food contact surface, and it complies with all standards of industry. Containers and wrapping films must also be pleasing in appearance and color to consumers.
Plastics used to make containers for microwavable food must have mechanical strength; that is, the packaging needs to be sturdy, rigid in shape, and capable of supporting the food within before and after microwave heating in conventional home (500 W) and restaurant/convenience store microwave ovens (1600 W). Packaging also needs to be heat resistant and capable of withstanding temperatures of up to 230° F. (110° C.) for microwave ovens and up to 400° F. (210° C.) for dual oven applications.
While the electromagnetic radiation used in microwave ovens does not directly interact with the packaging, food products that contain oils and fats can create localized temperatures of as much as 300° F. (150° C.) on the container surface. This localized heating may result in polymer degradation or conformation changes. Thus, the packaging should also maintain its visual appearance after heating in a microwave oven and should resist migration into food substances. For example, a conventional lid for a microwave food container must be sufficiently transparent so that the food product inside the package is visible. Typically, the lid may be fabricated from general purpose polystyrene, which has a heat distortion temperature (HDT) of 90° C. Such a lid is prone to deformation in the presence of oily food products, for example, because oily food products may generate heat upon warming in a microwave oven.
As a result, a need remains for microwavable food packages and food wrapping films. In particular, there is a need for polymer materials that can be used for food packaging that maintain their physical characteristics and that remain transparent after being heated in a microwave oven.